Inductively coupled compensator



INDUCTIVELY COUPLED COMPENSATOR Filed June 14, 1945 2 SHEETSSHEET l Elm/6mm EMERICK TOTH WKM LW March 4, 1952 E. TO' FH INDUCTIVELY COUPLED COMPENSATOR Filed Julie 14. 1945 2 SHEETSSHEET 2 gnaw/tom TOT H EMERICK Patented Mar. 4, 1952 UNITED STATES PATENT OFFICE 7. Claims.

(.Granted under the act of amended April 30', 1928;

I This: invention relates to means for coupling.

between heterodyne oscillators and converters and more particularly toward means for maintaining optimum oscillator voltage injection into theconverter of an ultra-high-frequency receiver of: the superheterodyne type, throughout the entire tuning range.

In receivers of the superheterodyne type it is wellknown to employ an oscillator, the' electrical oscillationsof which are coupled into a converter which mixes the oscillator frequency with the incoming signal, and produces a constant differ.- ence or intermediate frequency, which is passed on to the intermediate-frequency amplifier.

A commonly employed means for coupling os cillator and converter utilizes electro-magnetic induction between adjacent coils which form a part-of the oscillator and converter. tank circuits respectively. The oscillator circuit employed may be conventionally of eitherthe Hartley orColpitts types, While the converter may be of the gridleak biastype;

In the grid-leak type of converter the plate voltage utilized is sufficiently small so that the grid conducts on the positive peaks of theimpressed voltage oscillations; and, generally, the optimumconversion-point results when the. negative bias on the grid is slightly less than the peak oscillator voltage. Even without the application of oscillatorvoltag'e-the gridis normally biased negatively duerto the accumulation of electrons onto the grid from the space change between the cathode and plate of the converter tube: This may be termed the threshold bias. At-the optimum conversion point grid conduction occurs on the positive peaks of the impressed oscillator voltage; When grid conduction occurs the grid acquires an additional negative bias automatica'lly, as a result of the combined action of the grid capacitor andgrid resistor. The total negative bias then is sufficient to just permit conduction on the positive peaks of the oscillator voltage. For example, it has been found that the oscillator voltage should somewhat exceed approximately /2 volts when applied to a type-955 converter tube. in order to exceed the threshold voltage; and, preferably should be approximately from 1.0 to 2.0 volts'to operate at the optimum conversion point.

In prior art devices of this'class the oscillator voltage coupled intov the converter stage has varied over the range of ultra-high-frequencies to which the receiver was responsive. This was due to two factors: (1) The. oscillator develops lfes s voltageat the;lowfrequency end. of therange Marchv 3, 1883, as 370 O. G. 757) than. at the high frequency end of the range.

In general this is caused by the variation in the tank circuit characteristics, particularly (L/C), and Q, over the aforesaid frequency range. (2) Since the signal frequency and oscillator frequencies differ by a smaller percentage at'the high frequency end of the range the oscillator and converter tank circuits are more nearly in tune; and consequently energy transfer is more effective at the high frequency end of the range.

As above-mentioned there is a minimum peak oscillator voltage equal to the threshold bias appearing on the converter grid below which conversion efiiciency is decreased. In the same way there appears to be a maximum peak oscillator voltage appearing on the converter grid beyond which, any further increase in peak oscillator voltages will result in excessive radiation.

It is thus desirable to maintain a constant oscillator voltage input'into the converter, the oscillator voltage being maintained within: an optimum operating range.

It is accordingly an object of this invention to" provide for the injection of a substantially constant oscillator voltage onto the converter grid over a wide frequency range.

Another object of this invention is to provide means for supplying, oscillator voltage to a converterso as to effect its operation under constant optimum conversion efiiciency.

A further object of this invention is to provide a-novelcoupling system between oscillator and converter systems.

A still. further object of this invention is to provide for an. auxiliary or parallel compensating coupling means between oscillator and con-' verter circuits to maintain. constant injection of oscillator voltage into the converter over the entire frequency range of the receiver.

Another object of this invention is the injection into a converter of a constant oscillator voltage the magnitude of which is sufficiently small to avoid undesired radiation, yet sufficiently large to permit the peak oscillator voltage to exceed the threshold negative bias of the converter tube.

Still another object of the invention is toprovide novel coupling means betweentwo adjacent tank circuits to maintain a constant coupling between the said tank circuits, over an extended frequency range.

Other objects, features and advantages of the invention. will become apparent from the following detailed description. of a preferred embodiment thereof, taken in conjunction with accompanying drawings, in which:

Fig. 1 is a top plan view showing a converter and oscillator tank circuit units constructed and coupled according to the principles of this invention;

Fig. 2 shows a side elevational view of the converter and oscillator units shown in Fig. 1 coupled according to this invention;

Fig. 3 represents a section taken substantially on the line 3-3 of Fig. 2;

Fig. 4 shows a schematic diagram of a superheterodyne receiver employing the improved oscillator and converter units which are constructed in accordance with this invention;

Fig. 5 shows the relation between the conversion transconductance of the converter tube and 2 the peak oscillator voltage on the grid of the converter tube;

Fig. 6 shows the relation between the peak oscillator voltage and signal frequency, and illustrates the equalizer principle;

Fig. '1 shows experimental results obtained with a certain superheterodyne receiver constructed in accordance with one embodiment of this invention; and Fig. 8 is a detail view, slightly enlarged, of the adjustable plug member. Referring more specifically to Figs. 1, 2 and 3 of the drawings, there is shown an ultra-highfrequency converter tank circuit l6 comprising a three-element capacitor and inductor arms [4 and I5 formed integral with tank inductor I6 of generally U-shaped formation. portion of the capacitor unit [6 comprises two sets of stationary metal plate elements, viz., stationary plates 11, I8, 19 and 20 mounted on the end of inductor arm I5, and stationary plates 21, 22, 23 and 24, mounted on the end of inductor arm I4, respectively. End plates 36 and 31 of insulating material, secured in spaced relationship by means of insulating spacers 35, 35 and suitable bolts to the outer sides of the inductor arms l4 and I5, support anti-friction bearings 4| and 42, within which rotatable shaft 41 is free to rotate. Movable capacitor plate elements 25-34 are mounted on shaft 41 for rotation therewith. As thus arranged, the capacitor plate elements of the rotor are insulated from the fixed capacitor elements of the stator by the insulating end support members 36 and 31.

Unit I2 is the tank circuit of the ultra-highfrequency oscillator and is constructed similarly to unit I6 in that stationary capacitor plates 48, 49, 50, 5| are carried by the inductor arm 56 and stationary plates 52, 53, 54, 55 are carried by the inductor arm 56, respectively. Rotor shaft 46 is rotatably journaled in anti-friction bearings 39 and 40 which are mounted in spaced insulating support members 43 and 44, respectively. Mounted upon the rotatable shaft 46 are the movable metal plate elements 60-69 inclusive forming the capacitor rotor. The extended end of shaft 46 indicated as 46' may be turned by means of a suitable tuning dial (not shown) suitably secured thereto to control the angular positions of the rotor capacitor plate elements as well as indicate the frequency setting to which the receiver is tuned. The inner opposed ends of shafts 46 and 41 are mechanically interconnected, for example, by means of an Oldham type coupling 45 the intermediate member 45B of which may comprise an electrical insulating material, such as vulcanized rubber. As illustrated, the Oldham coupling consists of three members, flange element 45A and 45C keyed to the respective shafts 41-and46 and the central disc The stator 453 which engages each of said flanges by a feather and groove forming a sliding pair in the event of any misalignment of shafts 46 and 41. These pairs of feathers and grooves are at right angles to each other so that motion can be transmitted from one shaft to the other, the three members forming this coupling thus have the same angular displacement for all positions.

In accordance with the arran ement abovedescribed, the stationary capacitor plates 2 l-24 and 11-20, which are mounted on inductor arms I4 and I5 respectively, are supported on the ends of the U-member l6 which forms a single-turn inductance element associated with capacitor unit 10. Likewise, capacitor unit 12, including stationary capacitor plates 48-55, inductor arms 56 and 58 and U-member 51 is similarly constructed. Various points on each of the inductance elements l6 and 51 may be utilized as input and output terminals of the respective tank circuits and in one preferred embodiment of this invention the lower part of the inductance elements l6 and 51 is mounted upon the chassis or base I and suitably grounded thereto. This effectively grounds the. midpoint of the inductance element which together with the associated capacitor elements comprises a tank circuit. Angular and axial positioning of the movable capacitor elements 25 to 34 inclusive of unit It] with respect to the control shaft 41 is provided by mounting the group of capacitor plates upon sleeve which is carried by shaft 41. The sleeve 90, which has a sliding fit on the shaft 41, is suitably secured to the shaft 41-as by means of a tightening screw 92 mounted in a tapped portion 9| of the sleeve. In this way there is provided means for adjustably positioning the movable capacitor plates relative to both the fixed capacitor plates of the respective stators I4 and I5 and to the shaft 41. The movable capacitor elements Ell-69 of unit I2 are mounted upon the shaft 46 in a manner similar to the arrangement of'unit II], by means of sleeve 90', tapped portion 9| and tightening screw 92'.

The radio frequency input may be applied at terminal connector 30 of the converter tank unit l0, and the output to the grid of the converter may be taken from terminal connector: SI of the converter tank unit l0. 2

Similarly, the oscillator tube circuit may be connected to the oscillator tank unit 12 at terminals 82 and 83..

In addition to the mechanical coupling element 45 which gang-connects the movable capacitor plates of units I0 and I2, there is provided also an electrical equalizer network, such as coiled inductor 10, which is in a stand-off relation and turns with the shafts "46 and 41 as well as being electrically connected to the ends thereof. The purpose of the inductance 10 will be described more fully hereinafter.

Mounted within the main U-shaped inductor I6 is a small single-turn metal loop 15 which may be rotatably positioned at various angles with respect to the inductance element I6 by means of the adjustment screw 16 formed'integral with the loop 15, the loop 15 serves as a short-circuiting loop for the purpose of varying the inductance of the inductor 16. The adjusted position of loop 15 to which it is swung within inductor I6 is usually determined in the initial alignment of the unit I0 and is not subsequently disturbed in the ordinary operation of the receiver". For the purpose or adjusting the inductance of the U-shaped inductor 61 a movable single-turned of this screw advances or retracts a: metal" cylinder or plug 81 in the cylindrical bore formed between the concave opposed end faces of the flange members 8 1 and 85 extending.

from the underside of the separated inductor arms of the unit I2. The exterior of the plug 81' is provided with an insulating surface coating, such as a glass enamel 86 (see Fig; 8). Turning of adjusting screw 88 enables the" capacity' to be minutely varied by either withdrawal or in ertion of varied aniounts of metal forming the plug 81' between the extending flanges 34 and 85 of the respective inductor arms 56' and 58 which thus function as the plates-o'f'the trimming capacitor. Screw 88 turns within the outwardly projecting tapped metal sleeve 89 mounted upon the insulating support 89' which, in turn, is attached by suitable screwsto the adjacent side faces 56 and 58 of the se arated inductor arms 56and 58 of the unit I2. Similarly, converter unit Ill is provided with an'adjustable slug type trimming capacitor, designated by corresponding referencenumerals, inassociationwith the inductor arms I4 and I5 and the inductor IE thereof.

In Fig. 4, there is shown an ultra-high-frequency superheterodyne receiver constructed in accordance with the teachings of. this: invention. thisv arrangement input coaxial line I'I'UleadS to" end terminal II9 on inductor III of tuning unit I I IA, this unit being similar except for positions of the connections to the inductor III to the portion of Fig. 1 shown therein as unit II]. For purposes of clarifying the understanding of the operation of the system of Fig. 4 the schematic circuit diagram there represented shows the inductor III as comprising a coil having numerous turns which are appropriately tapped such as, for example, at IIE) for the input from the coaxial cable (I from the antenna, at. the midpoint I to ground, and at I2I where the output is taken from the tuning unit IIIA into the radio'frequency amplifier within its shielded box I81. The angular position of inductor H2, which corresponds to loop 15 of Fig. 2, with respect to inductor I II may be varied to align the tuned circuit. element capacitor there indicated comprises a movable set of capacitor plate elements II1 insulated. from the fixed capacitor plate elements H5 and H6. The capacitance may be varied, between the fixed plate elements of the threeelement capacitor, by relative motion of the rotor plates, I11 with respect to the fixed or stator capacitor element H5 and H5. Shunted across the fixed elements I I5 and I I5 is a fixed capacitor I'I3 which represents the distributed capacity of the inductor II I, plus an added loading capacitor, and also in shunt with the fixed elements I1 and I I6 is a secondcapacitor' I It which serves as a trimmer capacitor and corresponds to the-adjustable plug81 of Fig. 2.

The tank circuit unit IA of the radio fre quency amplifier within shielded box I81 is of similar construction to that previously described in connection with the tank unit IIIA within shielded box I86. The output of inductor l25 is In tuning unit IlIA the threepied to the movable removedat tap I24 and the radio frequency energy is fed through coupling capacitor I33 to the control grid of the radio frequency amplifier pento'de I39 which may comprise, for example, a type-956 tube. Voltage for automatic volume control purposes is introduced through afilter network formed by'resistors I34 and I35 and capacitor I36, and the radio frequency gain is controlled through the introduction of a suitable voltage through a filter network consisting of capacitors I38, I40 and resistor IIlI. Screen and suppressor grids of tube I39 are connected as shown, in the conventional manner. Plate voltage (+200 volts) is supplied through resistor I46 and the radio frequency voltage is passedthrough capacitor I41 into the end tap I48 on inductor I5! of converter tank circuit I5 IA. Itis to be again understood that theinductor I5I, which is shown for the sake of clarity of illustration as a multiple-turn coil, actually may comprise but a single turn loop; and that the invention is not limited to inductors of any specific number of turns, but the practical embodiment shown in Figs. 1-3 inclusive is the referred construction.

Continuing further with the description of Fig. 4" the oscillator'in'ductor H! of the oscillator tank circuit I1IA, there shown, which is representative of inductor 51 (see Fig. 2) and included inv the tank circuit I2, is grounded at its midtap I 12, and the outer terminals of inductor I H are connected through coupling capacitors I and I8I to the plate and grid terminals, respectively, of the oscillator tube I83 which may, for example, comprise a-type-955 tube. The control grid of tube I83 is connected through. grid resistor I82 to ground. Plate voltage (+150 volts) is supplied through resistor I84 and capacitor I85 which bypasses the radio frequency to ground preventing the latter from entering the power system. Inductor loop I13 may be rotated to adjust the inductance of the inductor Ii. The oscillator three-element-capacitor unit comprises fixed stator plates I15 and I16 and movable plate element I11. The movable plate element I1? is mechanically couplate element I58 of the threeelement-capacitor unit included in the converter tank circuit ItIA, by an Oldham or other type insulated coupling, such as 45 shown in Figs. 1 and 2, and indicated schematically in Fig. 4 by the broken interconnecting lines I18. Movable plate elements I11 and I58, in addition to the mechanical coupling I18, are electrically coupled through an impedance 18A which preferably may comprise the coiled inductor iii such as shown in Figs. 1 and 2. It is also within the purview of this invention. to employ other equalizing electrical networks thanthe impedance 18A, if desired, as will be apparent from the foregoing description. The oscillator tank circuit shown in Fig. 4 is inductively coupled through the proximity of inductor I-II of the oscillator tank circuit I1 IA to the inductor I5I in the converter tank circuit IEIA. The transfer of electromagnetic energy through the space between inductors I1! and I5I is most effective at the higher frequencies, since the two tank. circuits differ in their resonant frequencies by small percentage of the average frequency of the two tank circuits. Also,,at the upper end of therange theQ value of the oscillator tank circuit is greater and consequently a higher voltage is generated thereby transferring agreater voltage throughspace by induction to the converter-tank circuit.

To compensate for the lower voltage delivered by the: oscillator. to the converteca separate path, through impedance 10A, is provided in shunt with the mutual inductance path. The

.compensating action of this electrical path 'Under the latter condition the movable plates I58 and I1! are enmeshed to the greatest extent between their fixed stator capacitor elements I56, I51 and I15, I16, respectively, and therefore the net capacitative coupling between the two tank units is thereby increased. Also the value of the impedance 10A is reduced at lower frequency. The results of these two effects is to increase the coupling along the path through impedance 19A between the converter and the oscillator stages. The value of the impedance 10A may be selected as to substantially compensate for reduced electromagnetic coupling and reduced oscillator voltage output at lower frequencies.

It is to be understood that the above illustration is not limiting but that the principle of an equalizer network in shunt with electromagnetic coupling through the space between two tank circuits may take on other forms and yet come within the purview of this invention.

The oscillator circuit shown in Fig. 4 is of the Hartley type and the converter there shown is of the grid-leak bias type. It is also to be understood that these circuits are purely illustrative of the principles employed and are not to be considered limiting. The grid-leak bias type converter shown herewith is of a well known conventional type and need not be further described in detail. The intermediate frequency is transmitted from the primary I61 of the intermediatefrequency transformer to the secondary I68 thereof from which the intermediate-frequency line I69 leads to the intermediate-frequency amplifier (not shown).

It will be noted that the elements comprising the various tank circuits are ganged-connected, as indicated by broken lines I'I8A, so that unicontrol of these circuits is achieved. Thus, there is provided a novel and efficient superheterodyne receiver for reception in the ultra-high frequency range, which possesses a stability and constancy of operation and which radiates a minimum of energy.

Turning to Fig. 5, there is shown curve I which represents the transconductance at in micromhos of aconverter tube plotted against the peak oscillator voltage E on the grid of the tube.

The conversion transconductance ge is defined as the ratio of the magnitude of the intermediate-frequency beat component fr-fo of the output current to the magnitude of the input voltage of radio frequency fr, measured under the condition that all direct voltages and the magnitude of the input voltage at the oscillator frequency is are constant.

In Fig. is illustrated a threshold voltage region A in which the conversion transconductance is small. In the particular case of a type-955 tube the threshold voltage is. approximately minus one half volt (0.5 volt). The region denoted by the letter C represents relatively large peak oscillator voltages which result in excessive radiation. Between the two regions A and C is an optimum operating range ;which is herein denoted by the letter B from /2 to approximately 2.25 volts. In certain cases, the conversion transconductance curve is found to reach a maximum within the optimum operating region B.

In Fig. 5 the line aa' indicates a quantity called the maximum conversion transconductance which in that curve corresponds to approximately two volts peak oscillator voltage. It is desirable not only to obtain maximum conversion transconductance in order to obtain the largest possible intermediate frequency output from a given radio frequency signal input but also to maintain this maximum response throughout the entire frequency range. It will be understood that the curve I of Fig. 5 is purely illustrative and approximates conditions obtained when a type-955 tube is utilized as a converter tube in a grid-leak type converter circuit in which the plate voltage is maintained at approximately 30 volts relative to the cathode. Under these conditions the tube and circuit act as a diode-biased amplifier. A grid-leak type of converter circuit is utilized herein as the preferred form since. it operates well on low input voltages.

In Fig. 6, there are shown curves II, III and IV depicting peak oscillator voltage E0 plotted versus the frequency of the input radio frequency signal fr. Thus, curve IV shows peak oscillator voltage E0 ideally maintained at the maximum conversion transconductance corresponding to aa' throughout the entire frequency range. Curve III shows the variation in peak oscillator voltage throughout the frequency range of the receiver as obtained without the use of an equalizer network between the converter and the oscillator. Curve II shows the characteristics of the equalizer network required to produce with curve III the resultant curve IV. Regions A, B, and 0 each have the same meaning above stated in connection with Fig. 5.

In Fig. 7 there are shown two curves depicting peak oscillator voltage F30 plotted versus the frequency fr to which the receiver is tuned, showing results experimentally obtained in a certain superheterodyne receiver constructed in accordance with a specific embodiment of this invention. Curve V shows results obtained utilizing as the only coupling, that of mutual induction through the space between the tank circuits of the oscillator and the converter. It will be noted that particularly at low frequencies the conversion transconductrance of the converter tube is low and consequently the converter is operating inefficiently. In Fig. '7 the line aa as in both preceding figures again represents maximum conversion transconductance. The curve VI shown in Fig. '7 represents results obtained with a simple inductor coupling coil between the floating capacitor elements of the tube tank circuits, the tank circuits in addition are electromagnetically coupled through the intervening space. It will be noted that the variation in transconductance is reduced since the range of variation of curve VI is such as to cause a predominant operation within a substantially fiat region of the transconductance curve shown in Fig. 5. It will be also noted that the operation occurs at or in the neighborhood of the maximum transconductance. It will be understood that other types of equalizer coupling means which are operable to cause the curve VI to move closely approximate the proximity to the line art, may be employed in'place of the herein illustrated inductor coil 10 of Figs. 1 to 3 and impedance 10A of Fig. 4.

By way of example, typical values of the components employed in the oscillator and converter tank circuits may be as follows: The inductors l5l and I'll may have approximately .03 microhcnries. Thethree-element capacitor unitsmay have a minimum capacity of approximately 2 micromicrofarads and a maximum capacity of approximately 43 micromicrofarads. In addition, the stray capacity associated with the components connected to the tank circuits herein described may be of the order of 12 micromicrofarads. These values are intended to be illustrative only-and are not to be considered :aslimiting in any way.

Equalizer networks are known in the prior art capable of maintaining a source of energy at constant power level over a range of frequencies. A reference in this connection is Communication Engineering by Everitt, 2nd edition, Mc- Graw-Hill Book Company, 1937, pages 283 to 300 inclusive Certain general theorems are therein given which enable the construction of equalizer networks to compensate for known variations throughout a frequency range.

.It is within the purview of this invention to apply any such general type equalizer network between the floating capacitor elements of two tank circuits substantially in the arrangement described in this specification in lieu of the coil inductor 10 or impedance 10A.

In certain embodiments of this invention, for example, as shown in Fig. 4, the tank circuit is groundedat the midpoint, and the equalizing network is coupled off from the electrically floating plate elements of the capacitor unit which comprises a part of the tank circuit. It may seem that no power could be coupled through the floating element since it may appear that the floating element is at the potential of the midpoint, which is grounded. However, an unbalance is actually introduced into this system by the tube elements coupled to each side of the tank circuit which thus introduces a different impedance on each side of the tank circuit. The unbalance so produced at the floating electrical capacitor element with reference to ground permits a transfer of energy through the floating elements and their associated coupling circuit.

It is also contemplated to dispense with the electromagnetic coupling through the space between the oscillator and the converter tank units, and to provide instead a suitable coupling network between the floating capacitor elements of the oscillator and converter tank units as the only path between the aforesaid tank circuits. This may be accomplished by suitably shielding one tank circuit from the other by shields 200 and 28I shown in Fig. 4 for example, and by including the coupling network between the two floating capacitor elements substantially in the manner described in this specification. However, in order to obtain adequate power transfer between the oscillator and the converter it may be necessary to introduce a certain additional unbalance between the floating element and ground. This may readily be accomplished by reducing the impedance between one end of the tank circuit and the floating electrical capacitor element to ground by any known means, as for example, varying the value of one or the other capacitors which act to couple the tank circuit to the tube elements. In this case, since the electromagnetic space coupling path is not employed to supplement the network coupling path, the network coupling path should have a characteristic which compensates for the variation in voltage across the oscillator tank circuit throughout the frequency range.

While the invention has been described in con- (iii nection with a particular embodiment, certain variations have been suggested and it is to be understood that many additional changes are possible within the scope of the invention.

The invention described herein may be manufactured and used by Or for the Government of the United States of America for governmental purposes Without the payment of any royalties thereon or therefor.

What is claimed is:

1. In combination, two capacitor units each comprising three sets of capacitor plate elements, one of said sets being movable and the remaining two sets being fixed, the area of the said movable sets being such as to be capable of in: troduction in variable amounts in interleaving relationship between the two fixed elements of each unit, capacitive means providing a mechanical insulating coupling between said movable set of plate elements of the two capacitor units, and impedance means electrically coupling said movable sets of plate elements to each other, the said movable sets of plate elements floating electrically between said fixed set of plate elements.

2. In combination, two capacitor units, each of said units comprising three sets of capacitor plate elements, one of said sets being movableand the remaining two sets being fixed, the area of the said movable sets being such as to be capable of introduction in variable amounts in interleaving relationship with respect to the two fixed. sets of each unit, capacitive means pro-1 viding a mechanical insulating coupling be tween said movable sets of plate elements ofthe said capacitor units, and inductor means electrically coupling said movable sets of plate elements to each other, the said movable setsof plate elements floating electrically between said fixed sets of plate elements.

3. In combination, two capacitor units each'v comprising three sets of capacitor plate elements;

one of said sets being movable and the remaining sets being fixed, the area of the said movable sets being such as to be capable of introduction in variable amounts in interleaving relationship with respect to associated fixed sets of each unit, capacitive means providin a mechanical insulating coupling between said movable sets of plate elements of the said capacitor units, impedance means electrically coupling said movable sets of plate elements to each other, said movable sets of plate elements floating electrically between said fixed sets of elements, an inductor connected to each of said capacitor units to form a pair of tank circuits, and means electrically shielding said tank circuits from each other.

4. In combination, two capacitor units, each comprising three sets of capacitor plate elements, one of said sets being movable and the remaining two sets being fixed, the area of the said movable sets being such as to be capable of introduction in variable amounts in interleaving relationship with respect to the two fixed sets of each unit,

, capacitive means providing a mechanical insulating coupling between said movable sets of plate elements of said capacitor units, equalizer impedance means electrically coupling said movable sets of plate elements to each other, each of said movable sets of plate elements floating electrically between said associated pair of fixed sets of plate elements, an inductor associated with each of said capacitor units, said capacitor units mounted integrally with said associated inductors to form a pair of tank circuits which are electro- 7 magnetically coupled through the intervening space and means producing an electrical impedance unbalance at the said movable sets of elements with reference to ground.

5. In combination, two capacitor units, each comprising three sets of capacitor plate elements, one of said sets being movable and the remaining two sets .being fixed, the area of the said movable sets being such as to be capable of introduction in variable amounts in interleaving relationship with respect to the two fixed sets of each unit, capacitive means providing a mechanical insulating coupling between said movable sets of plate elements of said capacitor units, equalizer impedance means electrically coupling said movable sets of plate elements to each other, said movable sets of plate elements floating electrically between said associated pair of fixed sets of plate elements,

an inductor associated with each of said capacitor units, said capacitor units mounted integrally with said associated inductors to form a pair of tank circuits, means electrically shielding said tank circuits from each other, and means producing an electrical impedance unbalance at said movable sets of plate elements with reference to ground.

6. In combination, a pair of tuned circuits, each of said circuits including an inductance and a capacitance unit, each of said capacitance units comprising three sets of capacitor plate elements, one of said sets of each of said units being movable and the remaining two associated sets being fixed, the area of each of said movable sets being such as to be capable of introduction in variable amounts in interleaving relationship between said two associated fixed sets, capacitive means providing a mechanical insulating coupling between said movable sets of plate elements, and inductor means electrically coupling said movable sets of plate elements to each other, each of said movable sets of plate elements floating electrically between said two associated fixed sets.

7. In combination, a converter circuit, an os-' cillator circuit, each of said circuits including an inductance and a capacitance unit, each of said capacitance units comprising three sets of capacitor plate elements, one of said sets of each of said units being movable and the remaining two associated sets being fixed, the area of each of said movable sets being such as to be capable of introduction in variable amounts in interleaving relationship between said two associated fixed sets, capacitive means mechanically coupling said movable sets of plate elements together so as to revolve in unison, and inductor means electrically coupling said movable sets of plate elements to each other, each of said movable sets of plate elements floating electrically between said two associated fixed sets.

EMERICK TOTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 7 1,938,334 Hofiman Dec. 5, 1933 1,955,093 Roosenstein Apr. 17, 1934 2,001,694 Farnham May 14, 1935 2,159,782 Conklin et al. May 23, 1939 2,194,696 Eickemeyer et al. Mar. 26, 1940 2,244,807 Schrumpf June 10, 1941 2,266,670 Winfield Dec. 16, 1941 2,341,345 Van Billiard Feb. 8, 1944 2,384,504 Thias Sept. 11, 1945 2,404,669 Tillman July 23, 1946 2,408,895 Turner Oct. 8, 1946 2,422,454 Weiss June 17, 1947 2,453,489 Bruntil Nov. 9, 1948 FOREIGN PATENTS Number Country Date 405,175 Great Britain Feb. 1, 1934 

